Synthesis of β-diketiminate-ligated bimetallic and monometallic lanthanide amide complexes and their reactivity with isoprene and AlMe 3

Article abstract of DOI:10.1039/c3dt52014e

The amine elimination of lanthanide tris(amide) complexes with the phenylene-bridged bis(β-diketiminate) ligands PARA^Me-H ₂, META^Me-H₂ and PARA^Pr-H ₂ (PARA^Me-H₂ = 2[2,6-Me₂C ₆H₃NHC(Me)C(H)C(Me)N]-(para-phenylene), META ^Me-H₂ = 2[2,6-Me₂C₆H ₃NHC(Me)C(H)C(Me)N]-(meta-phenylene), PARA^Pr-H₂ = 2[2,6-ⁱPr₂C₆H₃NHC(Me)C(H)C(Me)N]- (para-phenylene)), and the mono-β-diketiminate ligand L ^2,6-iPr2_Ph-H (2,6-ⁱPr₂C ₆H₃)NHC(Me)CHC(Me)N(C₆H₅)) afforded the bimetallic lanthanide amide complexes PARA^Me-{Ln[N(SiMe ₃)₂]₂}₂ (Ln = Y (1), Sm (2)), META^Me-{Y[N(SiMe₃)₂]₂}₂ (3), PARA^Pr-{Ln[N(HSiMe₂)₂]₂} ₂ (Ln = Y (4), Sm (5)), and the monomeric complexes L ^2,6-iPr2_Ph-Y[N(SiMe₃)₂]₂ (6) and L^2,6-iPr2_Ph-Y[N(HSiMe₂) ₂]₂ (7). In the presence of AlR₃ and on activation with 1 equiv. of [Ph₃C][B(C₆F₅) ₄], complexes 1-7 showed a high activity toward the 1,4-selective polymerization of isoprene. The heterometallic Y/Al methyl complex [L ^2,6-iPr2_Ph]Y[(μ-Me)₂AlMe₂] ₂ (8) was prepared to elucidate the real active precursor in the polymerization.

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Synthesis of β-diketiminate-ligated bimetallic and
monometallic lanthanide amide complexes and their
Cite this: Dalton Trans., 2013, 42, 16355
reactivity with isoprene and AlMe3†
Song Sun,a,b Hao Ouyang,a Yunjie Luo,*c Yong Zhang,a Qi Shena and
Yingming Yao*a
The amine elimination of lanthanide tris(amide) complexes with the phenylene-bridged bis(β-diketi-
minate) ligands PARAMe-H2, METAMe-H2 and PARAPr-H2 (PARAMe-H2 = 2[2,6-Me2C6H3NHC(Me)C(H)C(Me)N]-
(para-phenylene), METAMe-H2 = 2[2,6-Me2C6H3NHC(Me)C(H)C(Me)N]-(meta-phenylene), PARAPr-H2
=
2[2,6-iPr2C6H3NHC(Me)C(H)C(Me)N]-(para-phenylene)), and the mono-β-diketiminate ligand L2,6-iPr2Ph-H
(2,6-iPr2C6H3)NHC(Me)CHC(Me)N(C6H5)) afforded the bimetallic lanthanide amide complexes PARAMe
-
{Ln[N(SiMe3)2]2}2 (Ln = Y (1), Sm (2)), METAMe-{Y[N(SiMe3)2]2}2 (3), PARAPr-{Ln[N(HSiMe2)2]2}2 (Ln = Y (4),
Sm (5)), and the monomeric complexes L2,6-iPr2Ph-Y[N(SiMe3)2]2 (6) and L2,6-iPr2Ph-Y[N(HSiMe2)2]2 (7). In
the presence of AlR3 and on activation with 1 equiv. of [Ph3C][B(C6F5)4], complexes 1–7 showed a high
activity toward the 1,4-selective polymerization of isoprene. The heterometallic Y/Al methyl complex
[L2,6-iPr2Ph]Y[(μ-Me)2AlMe2]2 (8) was prepared to elucidate the real active precursor in the polymerization.
Received 24th July 2013,
Accepted 9th September 2013
DOI: 10.1039/c3dt52014e
www.rsc.org/dalton
bimetallic Rh(I) and/or Ir(I) pyrazolyl complexes were highly
active for the intramolecular dihydroalkoxylation reaction of
Introduction
Compared to monomeric complexes, bimetallic complexes are alkyne diol substrates.2n In contrast, the cooperative effect of
anticipated to exhibit a cooperative effect between two metal bimetallic lanthanide complexes remains far less explored. To
centers and/or nuclearity effects in organic transformation and date, only quite limited bimetallic lanthanide derivatives have
polymerization.1 Up to date, bimetallic complexes of main been reported, in which most complexes were employed as
group and transition metals have received considerable atten- neutral initiators for the polymerization of polar monomers
tion and have displayed a unique reactivity and selectivity such as lactides.5 Whereas, bimetallic lanthanide complexes
which is strikingly different to their mononuclear analogues.2 as cationic pre-catalysts remain scarce. Only one example with
For example, Marks et al. reported that the bimetallic titanium respect to isoprene polymerization using bimetallic lanthanide
(Ti2) and zirconium (Zr2) complexes supported by “constrained alkyl complexes has been reported while this paper is in
geometry” ligands showed an obvious cooperative effect in preparation.6
olefin (co)polymerization.3 Harder and co-workers described
Recently, we found that the phenylene-bridged bis(β-diket-
that the bimetallic β-diketiminate-ligated calcium and zinc iminate) ligands are promising dinucleating ligand sets which
complexes were efficient catalysts for the copolymerization of stabilize the bimetallic lanthanide amide complexes, and
cyclohexene oxide with CO2.4 Messerle et al. reported that the these complexes are efficient initiators for the ring-opening
polymerization of lactides.5h To investigate the structure–reac-
tivity relationship of the bimetallic lanthanide complexes in
the polymerization, a series of new bimetallic lanthanide
aKey Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow
amide complexes stabilized by the rigid phenylene-bridged bis-
University, Suzhou 215123, People’s Republic of China. E-mail: yaoym@suda.edu.cn;
(β-diketiminate) ligands was synthesized and characterized. It
Fax: +(86) 512-65880305; Tel: +(86) 512-65882806
was found that these bimetallic lanthanide amide complexes
could serve as highly active catalyst precursors in isoprene
polymerization. The essential role of the lanthanide amide in
the polymerization was also investigated. To our knowledge,
this is the first example with respect to the investigation of iso-
prene polymerization employing bimetallic lanthanide amide
complexes as pre-catalysts. Here we wish to report these results.
bInstitute of Functional Material, School of Materials Science and Engineering,
Shaanxi University of Technology, Hanzhong 723003, People’s Republic of China
cOrganometallic Chemistry Laboratory, Ningbo Institute of Technology, Zhejiang
University, Ningbo 315100, P. R. China. E-mail: lyj@nit.zju.edu.cn
†Electronic supplementary information (ESI) available. CCDC numbers 952927
(for 1), 952928 (for 2), 952929 (for 3), 952930 (for 4), 952931 (for 6), 952932 (for
7) and 952933 (for 8). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3dt52014e
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Elemental analysis, NMR spectroscopy and X-ray crystallo-
graphy confirmed the compositions of complexes 1–5, and
showed that complexes 1–5 are neutral, bimetallic and solvent-
Results and discussion
Synthesis and characterization
The amine elimination of Ln[N(TMS)2]3(μ-Cl)Li(THF)3 with free species, whereas complexes 6 and 7 are monomeric
PARAMe-H2, and METAMe-H2 in a 2 : 1 molar ratio in THF at species. Strong absorptions near 1550 and 1530 cm−1 in the
25 °C afforded the corresponding bimetallic lanthanide amide FT-IR spectra showed the delocalization of the CvN double
1
complexes PARAMe-{Ln[N(SiMe3)2]2}2 (Ln = Y (1), Sm (2)) and bond in the β-diketiminate backbone.7 In the H NMR spectra
METAMe-{Y[N(SiMe3)2]2}2 (3) in 65–85% isolated yields. The of complexes 1 and 3 (Fig. S1 and S2, ESI†), the signal of the
similar reaction of Ln[N(HSiMe2)2]3(THF)2 with PARAPr-H2 in a NH protons of the phenylene bridged bis(β-diketiminate) com-
2 : 1 molar ratio in toluene at 70 °C gave the corresponding pounds at about δ 13.0 ppm disappeared, and there was only
bimetallic lanthanide amide complexes PARAPr-{Ln[N- one singlet peak for the protons of the amide groups in the
(HSiMe2)2]2}2 (Ln = Y (4), Sm (5)) in 72–82% isolated yields, as high-field region (near δ 0.30 ppm), suggesting a high fluxional
shown in Scheme 1.
of the amide groups in solution at room temperature. In the
When L2,6-iPr2Ph-H was treated with 1 equiv. of Y[N(TMS)2]3- case of complex 4, the H NMR spectrum exhibited a doublet
(μ-Cl)Li(THF)3 in THF at 25 °C and Y[N(HSiMe2)2]3(THF)2 in at δ 0.12, 0.22 ppm and a singlet at 4.79 ppm with the inte-
toluene at 70 °C, the corresponding monomeric yttrium amide gration of 48 H and 8 H, respectively (Fig. S3, ESI†), which
complexes L2,6-iPr2Ph-Y[N(SiMe3)2]2 (6) and L2,6-iPr2Ph-Y[N(HSi- could be assigned to the methyl protons and the Si–H protons
Me2)2(THF)]2 (7) were obtained in 67% and 78% isolated of the –N(HSiMe2)2 groups, respectively, in the bimetallic
1
yields, respectively, as shown in Scheme 1.
yttrium complex PARA-{Y[N(HSiMe2)2]2}2.
Scheme 1 The synthesis of complexes 1–7.
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All of these complexes are thermally stable at ambient
temperature in an argon atmosphere, and are soluble in THF
and toluene, but sparingly soluble in aliphatic solvents such as
hexane and pentane. The single-crystal structures of complexes
1–4, 6 and 7 were determined by X-ray diffraction. Complexes
1–4 bear similar molecular structures, and they have a comple-
tely symmetric bimetallic structure, which is similar to that of
the previously reported complex 9 (Chart 1).5h Thus, only the
molecular structure of complex 2 is provided in Fig. 1. The
variation of the substitution and position on the ligand back-
bone showed little influence on the Ln–N (amide) σ-bond dis-
tances (the average values are 2.235(3) Å for 1 and 2.239(2) Å
for 3). Meanwhile, the backbone of the β-diketiminate unit
(NC3N) and the lanthanide atom form a stable six-membered
ring in a boat conformation, and the C3 and lanthanide atoms
are 0.19 and 1.29 Å for 1 and 0.24 and 1.49 Å for 3 out of the
plane defined by N1–C2–C4–N2, respectively. The distances
between the two lanthanide atoms are 9.19 Å for 1 and 8.35 Å
for 3, which are somewhat longer than that of 8.10 Å in
PBDIMe-[Y(CH2SiMe3)2]2(THF)2.6 However, the distance of Y1–
Y2 in complex 4 is 7.85 Å, which is obviously shorter than that
of 9.22 Å in complex 9 (Chart 1), and this might be attributed
to the less sterically demanding substituents of the amide
groups in complex 4.
Fig. 2 The ORTEP diagram of complex 7 showing an atom numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level and the hydrogen
atoms are omitted for clarity.
there is a ligated THF molecule in complex 7, which is due to
the less steric demanding nature of the N(HSiMe2)2 group
compared with the N(SiMe3)2 group. The Y–N bond lengths in
complexes 6 and 7 are comparable with the corresponding
bond lengths in complexes 1, 3 and 4, and in the monomeric
β-diketiminate lanthanide amides, when the difference in the
ionic radii is considered.8
The structure determination revealed that complexes 6 and
7 are desired monomeric β-diketiminate yttrium bis(amide)
complexes. The ORTEP diagram of complex 7 is shown in
Fig. 2. The structural difference in the two complexes is that
Isoprene polymerization
To test the polymerization activity of these bimetallic lantha-
nide amide complexes, they were employed as cationic catalyst
precursors in isoprene polymerization. These neutral bi-
metallic lanthanide amide complexes alone showed no activity
toward isoprene polymerization, and neither did the binary
catalytic systems formed from complexes 1–5/AliBu3 and from
complexes 1–5/[Ph3C][B(C6F5)4].9 However, in the presence of
excess AliBu3 and on activation with 1 equiv. of [Ph3C]-
[B(C6F5)4] to form the ternary catalyst system, they became
active for the 1,4-selective polymerization of isoprene in
toluene at room temperature. The results are summarized in
Table 5. It was found that the ancillary ligand had a significant
effect on the polymerization activity. The complexes bearing
the PARAMe ligand exhibited a higher activity compared with
those supported by the PARAPr and METAMe ligand. For
example, complex 1 achieved complete polymerization within
5 min (Table 5, entry 2), while complexes 3 and 9 only reached
28% and 34% yields even at a prolonged polymerization time
(Table 5, entries 6 and 26), indicating that the more crowded
metal center hindered the orientation and insertion of the
incoming monomer after the incorporation of one isoprene
molecule.10 On the other hand, the polymerization activity was
also dependent on the central metal. The observed activity
order for the bimetallic lanthanide amido complexes was,
complex 1 (Y) > complex 2 (Sm), complex 4 (Y) > complex 5
(Sm) (Table 5, entries 2 vs. 3, and 11 vs. 13), which might be
Chart 1 The molecular structure of complex 9.
Fig. 1 The ORTEP diagram of complex 2 showing an atom numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level and the hydrogen
atoms are omitted for clarity.
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attributed to the more Lewis acidic nature of the small radius borate resulted in the influence of the addition sequence of
lanthanide ions.11 When AlMe3 was used instead of AliBu3, the aluminum alkyl and borate on the polymerization.
polymerization activity decreased dramatically (Table 5, entries
Active species
7–8 vs. 10–11, and 18 vs. 22). Notably, when using the catalyst
system of complex 4/AliBu3/[Ph3C][B(C6F5)4], the increase of
isoprene to yttrium molar ratios from 500 to 3000 resulted in a
proportional increase of the molecular weights from 37.4 to
105.6 × 104 (Mn), while the molecular weight distributions kept
nearly constant (Mw/Mn = 1.80–1.86) (Table 5, entries 9–12,
Fig. S11, ESI†), suggesting a controllable polymerization
nature. Additionally, compared with the binuclear β-diket-
iminato yttrium system PBDIMe-[Y(CH2SiMe3)2]2(THF)2/AliBu3/
[Ph3C][B(C6F5)4],6 3/AliBu3/[Ph3C][B(C6F5)4] displayed a com-
parable activity, but it gave the resultant polymer with a higher
1,4-regularity (88.4%) (Table 5, entry 4). The GPC curves indi-
cated that all of the polymer samples produced by the ternary
catalyst systems were unimodal, which is indicative of a single-
site polymerization behavior. This is the first example with
respect to isoprene polymerization using bimetallic lanthanide
amide complexes supported by β-diketiminate ligands as cata-
lyst precursors upon to date.
To reveal whether these bimetallic lanthanide amide com-
plexes would exhibit a cooperative effect, the corresponding
monomeric counterparts 6 and 7 were also employed in iso-
prene polymerization for comparison. Unfortunately, under
the same polymerization conditions, no obvious difference
was observed in both the activity and selectivity using the
monomeric and bimetallic catalyst precursors (Table 5, entries
9–12 vs. 17–20, 14–15 vs. 25–26). This may be attributed to the
fact that the distances of the two metals in the above bi-
metallic complexes is out of the range where the two metals
could interact with each other.2n
In order to understand the essential role of the lanthanide
amide complexes, and to gain some information about the
active species in this polymerization, the reaction between
complex 7 and AlMe3 was carried out. The treatment of
complex 7 with excess AlMe3 in hexane at room temperature,
after workup, afforded the mono-diketiminate-ligated Y/Al
heterodimetallic methyl complex [L2,6-iPr2Ph]Y[(μ-Me)2AlMe2]2
(8) in a 60% isolated yield, as shown in Scheme 2. The gene-
ration of complex 8 is subjected to the amide–alkyl exchange
as reported previously (Fig. 3).12 Remarkably, the NMR moni-
toring reaction of complex 8 with 1 equiv. of [Ph3C][B(C6F5)4]
in chlorobenzene-d5 revealed that the reaction took place
immediately (Scheme 3). In the 1H NMR spectrum, the reso-
nances of the methyl proton of the Al2Me8 ligand at δ
−0.15 ppm disappeared (Fig. S6, ESI†). Instead, three singlets
appeared at δ 2.10, −0.26 and −0.49 ppm with the integration
of 3H, 9 H and 12 H, which could be assigned to the methyl
protons of the newly generated Ph3CMe, AlMe3 and [L2,6-iPr2Ph]-
Y[(μ-Me)2AlMe2][B(C6F5)4], respectively (Fig. 4). The new signals
for the β-diketiminate ligand appeared shifted to a slightly
higher field in accordance with a stronger coordination toward
the highly electron-deficient rare-earth-metal cation.13 These
Different to the catalyst systems of the lanthanide alkyl
complex/AliBu3/[Ph3C][B(C6F5)4], in which the addition
sequence of [Ph3C][B(C6F5)4] and AliBu3 first to the lanthanide
complex showed hardly any effect on the polymerization be-
havior, the addition sequence would affect the polymerization
behavior of the lanthanide amide complexes with different
amide groups. For example, no obvious influence was observed
when [Ph3C][B(C6F5)4] was added first, and then AliBu3, or in
the reverse order using complex L2,6-iPr2Ph-Y[N(SiMe3)2]2 (6) as
a pre-catalyst (Table 5, entries 15 and 16). In contrast, the
polymerization completed in 3 min for complex L2,6-iPr2Ph-Y[N-
(HSiMe2)2(THF)]2 (7) when AliBu3 was added first, and then
[Ph3C][B(C6F5)4]; whereas the yield decreased dramatically
when [Ph3C][B(C6F5)4] was added first, and then AliBu3
(Table 5, entries 19 and 21). The NMR monitoring reaction of
complex 6 with 1 equiv. of [Ph3C][B(C6F5)4] in chlorobenzene-
d5 revealed that the reaction hardly took place even when the
reaction time was prolonged to 7 days, whereas the reaction of
complex 7 with 1 equiv. of [Ph3C][B(C6F5)4] took place
smoothly in a short time under the same conditions (Fig. S12
and S13, ESI†). These results revealed that the steric bulkiness
of the amido groups has a profound effect on the reactivity of
the corresponding β-diketiminate lanthanide amides. We pos-
Scheme 2 The formation of complex 8.
Fig. 3 The ORTEP diagram of complex 8 showing an atom numbering scheme.
Thermal ellipsoids are drawn at the 30% probability level and the hydrogen
tulated that the different reactivities of the amide groups with atoms are omitted for clarity.
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Scheme 3 The NMR scale reaction of complex 8 with 1 equiv. of [Ph3C][[B(C6F5)] (400 MHz, C6D5Cl + C6D6).
Fig. 4 The 1H NMR spectrum of the reaction of complex 8 with 1 equiv. of [Ph3C][[B(C6F5)4], 25 °C, after 30 min (400 MHz, C6D5Cl + C6D6).
results indicated that the combination of complex 8 with corresponding cationic β-diketiminate Ln/Al methyl species,
[Ph3C][B(C6F5)4] resulted in the formation of the cationic which was the true active species in the isoprene
β-diketiminate heterodinuclear Ln/Al species, which should be polymerization.
the true active species for the isoprene polymerization.14
Experimental section
General procedures
Conclusions
In summary, a series of bimetallic and monomeric lanthanide All manipulations were performed in a pure argon atmosphere
amide complexes stabilized by β-diketiminate ligands were pre- with the rigorous exclusion of air and moisture using standard
pared and well-characterized. In the presence of excess AlR3 Schlenk techniques and an argon-filled glove box. The solvents
and on activation with 1 equiv. of [Ph3C][B(C6F5)4], all these (toluene, hexane and THF) were distilled from sodium/benzo-
complexes could catalyze the 1,4-selective polymerization of phenone ketyl, degassed by the freeze–pump–thaw method
isoprene with a high activity in toluene at room temperature. and dried over fresh Na chips in the glove box. Anhydrous
Although a cooperative effect was not observed under the LnCl3 and [Ph3C][B(C6F5)4] were purchased from STREM.
present polymerization conditions, the polymerization activity AlMe3, AliBu3 and n-BuLi (2.5 M in a hexane solution) were
was found to be dependent on the ancillary ligand and central purchased from Acros and used as received. Isoprene was pur-
metal. The amide–alkyl exchange of the lanthanide amide chased from Acros, dried by stirring with CaH2 and distilled
complex with AlMe3 occurred to give the mono-diketiminate- before polymerization. The deuterated solvents (CDCl3, chloro-
ligated Ln/Al heterodimetallic methyl complex. This hetero- benzene-d5, C6D6) were obtained from CIL. The ligands
dimetallic complex was ready to be converted into the PARAPr-H2
=
[2,6-iPr2C6H3NHC(Me)C(H)C(Me)N]2-(para-
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phenylene),4 PARAMe-H2 = [2,6-iPr2C6H3NHC(Me)C(H)C(Me)N]2- concentrated toluene solution (about 20 mL) at 25 °C in a few
(para-phenylene),4 METAMe-H2 = [2,6-iPr2C6H3NHC(Me)C(H)- days (1.68 g, 65%). Mp: 228–231 °C. 1H NMR (C6D6, 400 MHz):
C(Me)N]2-(meta-phenylene),4 L2,6-2iPr2
= (2,6-iPr2C6H3)NHC- 7.16 (d, 4H, CHN-aryl), 6.97 (m, 6H, CHN-aryl), 6.51 (s, 1H, CHN-aryl),
Ph
(Me)CHC(Me)N(C6H5),15a Ln[N(TMS)2]3(μ-Cl)Li(THF)3 (Ln
Sm, Y)15b and Ln[N(HSiMe2)2]3(THF)2 (Ln = Sm, Y)15c were pre- CH3CN), 1.53 (s, 6H, CH3CN), 0.30 (s, 72H, TMS). 13C NMR
pared according to the literature. (100 MHz, C6D6): δ 5.0 (Si(CH3)3), 20.0 (Ar-CH3), 23.9 (CH3CN),
=
5.13 (s, 2H, CH3CNCH), 2.25 (s, 12H, Ar-CH3), 1.89 (s, 6H,
Samples of the organolanthanide complexes for the NMR 25.6 (CH3CN), 97.4 (CH3CNCH), 122.5 (CHN-aryl), 123.2
spectroscopic measurements were prepared in the glove box (CHN-aryl), 125.5 (CHNaryl), 129.1 (CHNaryl), 131.4 (CHNaryl),
using J. Young valve NMR tubes. The NMR (1H, 13C) spectra 147.1 (CHNaryl), 147.4 (CvN), 150.8 (CvN), 165.4 (CvN),
were recorded on a Varian Unity spectrometer at 25 °C. The 167.3 (CvN). FT-IR (KBr, cm−1): 3056 (s), 3030 (s), 2960 (s),
carbon, hydrogen and nitrogen analyses were performed by 2868 (m), 1625 (s), 1552 (s), 1515 (s), 1459 (s), 1430 (s),
direct combustion with a Carlo-Erba EA-1110 instrument. The 1382 (s), 1371 (s), 1282 (m), 1168 (m), 986 (w), 881 (s), 848 (s),
FT-IR spectra were recorded with a Nicolet-550 FT-IR spectro- 753 (m). Anal. calcd for C56H108N8Si8Y2: C, 51.90; H, 8.40; N,
meter as KBr pellets. The molecular weight and molecular 8.65. Found: C, 51.83; H, 8.61; N, 8.72.
weight distribution were determined against polystyrene stan-
PARAPr-{Y[N(HSiMe2)2]2}2 (4). A toluene solution of Y[N(HSi-
dards by gel permeation chromatography (GPC) on a PL 50 Me2)2]3(THF)2 (1.25 g, 2.00 mmol) was added dropwise into a
apparatus and THF was used as an eluent at a flow rate of toluene solution of PARAPr-H2 (10 mL, 0.59 g, 1.00 mmol). The
1.0 mL min−1 at 40 °C.
mixture was stirred overnight at 70 °C. The removal of the vola-
PARAMe-{Y[N(SiMe3)2]2}2 (1). A THF solution of Y[N(TMS)2]3- tiles under vacuum produced a light yellow powder. The result-
(μ-Cl)Li(THF)3 (3.31 g, 4.00 mmol) was added dropwise into a ing powder was dissolved in about 10 mL of hexane, and a
THF solution of PARAMe-H2 (0.96 g, 2.00 mmol) at room temp- small amount of the precipitate formed was removed by cen-
erature. The mixture was stirred at 25 °C overnight, and then trifugation. The solution was kept at room temperature over-
THF was evaporated completely under reduced pressure. night to give complex 4 as yellow crystals (1.06 g, 82%). Mp:
1
Toluene (35 mL) was added to the residue, and the mixture 213–215 °C. H NMR (C6D6, 300 MHz): 7.31 (s, 4H, CHN-aryl),
was stirred at 80 °C for about 12 h. After the precipitate was 7.09 (s, 6H, CHN-aryl), 5.19 (s, 2H, CH3CNCH), 4.84 (s, 8H,
removed by centrifugation, the resulting filtrate was dried com- SiHMe2), 3.13 (m, 4H, CH(CH3)2), 2.04 (s, 6H, CH3CN), 1.65 (s,
pletely under reduced pressure. Colorless crystals were 6H, CH3CN), 1.33 (d, 12H, CH(CH3)2), 1.15 (d, 12H, CH(CH3)2),
obtained from concentrated toluene solution (about 13 mL) at 0.17 (d, 48H, SiHMe2). 13C NMR (75 MHz, C6D6): δ 2.7
25 °C in a few days (1.89 g, 73%). Mp: 259–261 °C. 1H NMR (SiHMe2), 23.7 (CH3CN), 23.8 (CH3CN), 24.1 (CH(CH3)2), 24.2
(C6D6, 300 MHz): 7.24 (d, 4H, CHN-aryl), 6.96 (s, 6H, CHN-aryl), (CH(CH3)2), 28.6 (CH(CH3)2), 93.9 (CH3CNCH), 98.5
5.12 (s, 2H, CH3CNCH), 3.10 (m, 4H, CH(CH3)2), 2.23 (s, 12H, (CH3CNCH), 124.0 (CHN-aryl), 125.7 (CHN-aryl), 126.1 (CHNaryl),
Ar-CH3), 1.86 (s, 6H, CH3CN), 1.50 (s, 6H, CH3CN), 0.29 (s, 123.8 (CHNaryl), 126.2 (CHNaryl), 127.0 (CHNaryl), 141.9
72H, TMS). 13C NMR (75 MHz, C6D6): δ 4.7 (Si(CH3)3), 19.6 (Ar- (CHN-aryl), 143.1 (CvN), 144.1 (CvN), 163.6 (CvN), 167.8
CH3), 23.6 (CH3CN), 24.9 (CH3CN), 97.9 (CH3CNCH), 125.2 (CvN). FT-IR (KBr, cm−1): 3057 (s), 2960 (s), 2867 (m), 2110
(CHN-aryl), 126.8 (CHN-aryl), 128.9 (CHNaryl), 131.5 (CHNaryl), (m), 2069 (m), 1625 (s), 1552 (s), 1508 (s), 1461 (s), 1435 (s),
146.0 (CvN), 147.2 (CvN), 165.5 (CvN), 167.4 (CvN). FT-IR 1380 (s), 1363 (s), 1325 (m), 1276 (s), 1177 (s), 1100 (w), 855 (s),
(KBr, cm−1): 3053 (s), 3029 (s), 2961 (s), 2869 (m), 1625 (s), 787 (m), 757 (m). Anal. calcd for C56H108N8Si8Y2: C, 51.90; H,
1552 (s), 1515 (s), 1459 (s), 1435 (s), 1380 (s), 1368 (s), 1280 8.40; N, 8.65. Found: C, 51.85; H, 8.53; N, 8.72.
(m), 1165 (m), 998 (w), 887 (s), 840 (s), 756 (m). Anal. calcd for
C56H108N8Si8Y2: C, 51.90; H, 8.40; N, 8.65. Found: C, 51.81; H, was carried out in the same way as that described for complex
8.56; N, 8.69. 4, but Sm[N(HSiMe2)2]3(THF)2 (1.38 g, 2.00 mmol) was used
PARAPr-{Sm[N(HSiMe2)2]2}2 (5). The synthesis of complex 5
PARAMe-{Sm[N(SiMe3)2]2}2 (2). The synthesis of complex 2 instead of Y[N(HSiMe2)2]3(THF)2. Yellow crystals were obtained
was carried out in the same way as that described for complex from a concentrated toluene solution (about 8 mL) at 25 °C in
1, but Sm[N(TMS)2]3(μ-Cl)Li(THF)3 (3.56 g, 4.00 mmol) was a few days (1.15 g, 81%). Mp: 203–205 °C. FT-IR (KBr, cm−1):
used instead of Y[N(TMS)2]3(μ-Cl)Li(THF)3. Yellow crystals 3060 (m), 2960 (s), 2867 (m), 2111 (m), 2068 (m), 1626 (s), 1552
were obtained from a concentrated toluene solution (about (s), 1508 (s), 1460 (s), 1435 (s), 1380 (s), 1365 (m), 1276 (s),
15 mL) at 25 °C in a few days (1.96 g, 69%). Mp: 271–273 °C. 1257 (s), 1177 (s), 1100 (s), 1026 (m), 934 (s), 789 (s), 757 (m).
FT-IR (KBr, cm−1): 3060 (m), 2963 (s), 2892 (m), 2873 (s), 1625 Anal. calcd for C56H108N8Si8Sm2: C, 47.40; H, 7.67; N, 7.90.
(s), 1554 (s), 1510 (s), 1460 (s), 1435 (s), 1385 (s), 1360 (m), Found: C, 47.46; H, 7.81; N, 7.83.
1274 (m), 1256 (m), 1181 (w), 942 (s), 887 (s), 751 (m). Anal.
calcd for C56H108N8Si8Sm2: C, 47.40; H, 7.67; N, 7.90. Found: carried out in the same way as that described for complex 1,
L2,6-iPr2PhY[N(SiMe3)2]2 (6). The synthesis of complex 6 was
C, 47.51; H, 7.73; N, 8.03.
but L2,6-iPr2Ph-H (1.34 g, 4.00 mmol) was used instead of
METAMe-{Y[N(SiMe3)2]2}2 (3). The synthesis of complex 3 PARAMe-H2. Colorless crystals were obtained from a concen-
was carried out in the same way as that described for complex trated hexane solution (about 6 mL) at 25 °C in a few days
1
1, but METAMe-H2 (0.96 g, 2.00 mmol) was used instead of (1.99 g, 67%). Mp: 187–190 °C. H NMR (C6D6, 300 MHz): 7.19
PARAMe-H2. Colorless crystals were obtained from
a
(m, 3H, CHN-aryl), 7.09 (s, 4H, CHN-aryl), 6.98 (t, 3H, CHN-aryl),
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5.10 (s, 1H, CH3CNCH), 3.10 (m, 2H, CH(CH3)2), 1.80 (s, 3H, Anal. calcd for C31H57N4Si4Y: C, 54.19; H, 8.36; N, 8.15. Found:
CH3CN), 1.67 (s, 3H, CH3CN), 1.34 (d, 6H, CH(CH3)2), 1.10 (d, C, 54.23; H, 8.41; N, 8.26 (coordinated THF was removed
6H, CH(CH3)2), 0.29 (s, 36H, TMS). 13C NMR (75 MHz, C6D6): δ under vacuum).
5.17 (Si(CH3)3), 24.90 (CH3CN), 25.28 (CH(CH3)2), 25.82
L2,6-iPr2PhY[(μ-Me)2AlMe2]2 (8). A hexane (5 mL) solution of
(CH(CH3)2), 97.64 (CH3CNCH), 124.53 (CHN-aryl), 124.94 complex 7 (0.34 g, 0.5 mmol) was added dropwise to a heptane
(CHN-aryl), 125.66 (CHNaryl), 126.23 (CHNaryl), 128.92 (CHNaryl), solution (3 mL) of AlMe3 (3 mmol, 1.0 M) at room temperature.
142.02 (CvN), 145.51 (CvN), 149.79 (CvN), 164.74 (CvN), The reaction mixture was stirred at room temperature over-
167.67 (CvN). IR (KBr, cm−1): 3058 (m), 3029 (s), 2960 (s), night to give a pale white solution with a large amount of pre-
2866 (m), 1624 (s), 1596 (m), 1555 (m), 1504 (m), 1485 (s), 1437 cipitate. The removal of the volatiles under vacuum produced
(m), 1381 (s), 1363 (s), 1282 (m), 1102 (m), 1177 (s), 1028 (w), a pale white powder. The resulting pale white powder was dis-
933 (m), 840 (s), 760 (s). Anal. calcd for C35H65N4Si4Y: C, 56.57; solved in about 6 mL of a hexane–toluene (4/2, v/v) mixture
H, 8.82; N, 7.54. Found: C, 56.68; H, 8.93; N, 7.63.
and was kept at −30 °C overnight to give complex 8 as colorless
L2,6-iPr2PhY[N(HSiMe2)2]2 (7). The synthesis of complex 7 was crystals (0.18 g, 60%). Mp: 235–238 °C. 1H NMR (C6D6,
carried out in the same way as that described for complex 4, 400 MHz): 7.24 (m, 4H, CHN-aryl), 7.12 (m, 3H, CHN-aryl), 7.06
but L2,6-2iPr2Ph-H (0.67 g, 2.00 mmol) was used instead of (m, 1H, CHN-aryl), 5.21 (s, 1H, CH3CNCH), 3.13 (m, 2H,
PARA-H2. Colorless crystals were obtained from a concentrated CH(CH3)2), 1.71 (s, 3H, CH3CN), 1.64 (s, 3H, CH3CN), 1.37 (d,
hexane solution (about 4 mL) at 25 °C in a few days (1.07 g, 6H, CH(CH3)2), 1.06 (d, 6H, CH(CH3)2), −0.08 (s, 24H,
78%). Mp: 179–181 °C. 1H NMR (C6D6, 300 MHz): 7.21 (m, 4H, [AlMe4]−). 13C NMR (100 MHz, C6D6): δ 1.4 ([AlMe4]−), 23.8
CHN-aryl), 7.09 (s, 3H, CHN-aryl), 6.98 (m, 1H, CHN-aryl), 5.14 (s, (CH3CN), 25.0 (CH(CH3)2), 25.1 (CH(CH3)2), 26.0 (CH(CH3)2),
1H, CH3CNCH), 4.82 (m, 4H, SiHMe2), 3.12 (m, 2H, CH(CH3)2), 28.7 (CH(CH3)2), 100.7 (CH3CNCH), 125.4 (CHN-aryl), 126.1
1.85 (s, 3H, CH3CN), 1.64 (s, 3H, CH3CN), 1.34 (d, 6H, (CHN-aryl), 126.6 (CHNaryl), 127.6 (CHNaryl), 129.6 (CHNaryl),
CH(CH3)2), 1.14 (d, 6H, CH(CH3)2), 0.12 (d, 24H, SiHMe2). 13C 142.5 (CHNaryl), 143.0 (CvN), 149.3 (CvN), 166.7 (CvN),
NMR (100 MHz, C6D6): δ 2.9 (Si(CH3)3), 23.6 (CH3CN), 24.1 169.7 (CvN). Anal. calcd for C31H53Al2N2Y: C, 62.41; H, 8.95;
(CH3CN), 24.4 (CH(CH3)2), 24.5 (CH(CH3)2), 28.8 (CH(CH3)2), N, 4.70. Found: C, 62.50; H, 8.90; N, 4.75.
98.6 (CH3CNCH), 124.3 (CHN-aryl), 124.8 (CHN-aryl), 124.9
(CHNaryl), 126.4 (CHNaryl), 129.8 (CHNaryl), 142.3 (CHNaryl),
The typical procedure for the isoprene polymerization
143.3 (CvN), 147.4 (CvN), 163.7 (CvN), 168.1 (CvN). FT-IR
(KBr, cm−1): 3059 (s), 2960 (s), 2870 (m), 2109 (m), 2072 (m),
1625 (s), 1552 (s), 1510 (s), 1462 (s), 1438 (s), 1381 (s), 1365 (s),
1328 (m), 1275 (s), 1177 (s), 1100 (w), 855 (s), 786 (m), 753 (m).
The procedures for the isoprene polymerization catalyzed by
these lanthanide amides were similar, and a typical polymeriz-
ation procedure is given below. A 50 mL Schlenk flask
equipped with
a magnetic stirring bar was charged in
Table 1 The crystallographic data for complexes 1–4
Compound
1
2
3
4
Formula
fw
C56H108N8Si8Y2
1296.04
C56H108N8Si8Sm2
1418.92
C56H108N8Si8Y2
1296.04
C56H108N8Si8Y2
1296.04
T/K
223(2) K
Triclinic
0.60 × 0.40 × 0.20
ˉ
P1
223(2) K
Triclinic
0.50 × 0.18 × 0.12
ˉ
P1
220(2)
293(2)
Crystal system
Crystal size/mm
Space group
Orthorhombic
0.75 × 0.66 × 0.50
C2221
Monoclinic
0.55 × 0.35 × 0.10
C2/c
a/Å
b/Å
c/Å
α/°
11.1103(18)
11.4141(19)
15.307(2)
92.761(4)
92.247(3)
108.104(4)
1839.9(5)
1
11.2006(12)
11.4482(11)
15.2323(13)
92.946(2)
93.603(2)
108.289(3)
1845.6(3)
1
16.9447(7)
18.8097(9)
23.3593(11)
10.5762(8)
20.4287(10)
34.9745(18)
β/°
95.853(6)
γ/°
V/Å3
7445.2(6)
4
1.156
7517.1(8)
4
1.145
Z
Dcalcd/g cm−3
1.170
1.736
1.277
1.742
μ/mm−1
1.716
1.700
F(000)
θmax/°
690
25.50
736
25.50
2760
25.50
2760
25.50
Collected
Unique reflns
14 910
6792
15 907
6812
23 492
6861
19 022
6980
Obsd reflns [I > 2.0σ(I)]
No. of variables
4974
351
6104
351
5924
351
4464
300
GOF
R
wR
Rint
1.044
1.041
1.030
1.049
0.0473
0.1144
0.0411
0.703, −0.578
0.0316
0.0619
0.0372
0.731, −0.541
0.0348
0.0698
0.0463
0.528, −0.342
0.0843
0.2142
0.0678
1.587, −2.061
Largest diff. peak, hole/e Å−3
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sequence with the desired amount of the lanthanide amide,
toluene, borate (or triisobutylaluminum and borate) and iso-
prene. The mixture was stirred vigorously at room temperature
for the desired time, during which an increase of viscosity was
observed. The reaction mixture was quenched by the addition
of ethanol and then poured into a large amount of ethanol to
precipitate the polymer, which was dried under vacuum at
60 °C and weighed.
Table 2 The crystallographic data for complexes 6–8
Compound
6
7
8
Formula
fw
T/K
C
35H65N4Si4Y
C35H65N4OSi4Y
759.18
293(2)
C31H53Al2N2Y
596.62
293(2)
Monoclinic
0.80 × 0.70 ×
0.40
743.18
223(2) K
Crystal system
Crystal size/mm
Orthorhombic
0.60 × 0.40 ×
0.20
Orthorhombic
0.75 × 0.60 ×
0.20
Space group
Pbca
Pca21
P121/n1
a/Å
b/Å
c/Å
20.0835(9)
20.5924(12)
20.6268(10)
18.189(2)
14.5123(12)
16.414(5)
12.6433(12)
20.8974(18)
13.2484(13)
X-Ray crystallographic structure determinations
α/°
Suitable single crystals of complexes 1–4 and 6–8 were sealed
in a thin-walled glass capillary to determine the single-crystal
structures. The intensity data were collected with a Rigaku
Mercury CCD area detector in the ω scan mode using Mo Kα
radiation (λ = 0.71070 Å). The diffracted intensities were cor-
rected for Lorentz/polarization effects and empirical absorp-
tion corrections. The details of the intensity data collection
and crystal data are given in Tables 1 and 2.
The structures were solved by direct methods and refined
by full-matrix least-squares procedures based on |F|2. All of the
non-hydrogen atoms were refined anisotropically. The hydro-
gen atoms in these complexes were all generated geometrically,
assigned appropriate isotropic thermal parameters, and
allowed to ride on their parent carbon atoms. All of the hydro-
gen atoms were held stationary and included in the structure
factor calculation in the final stage of the full-matrix least-
squares refinement. The structures were solved and refined
using the SHELEXL-97 program. The selected bond parameters
are summarized in Tables 3 and 4.
β/°
98.252(3)
γ/°
V/Å3
8530.6(8)
8
1.157
1.506
3184
25.50
25 980
7897
4332.8(15)
4
1.164
1.486
1624
26.39
24 412
8388
3464.1(6)
4
1.144
1.754
1272
25.35
33 231
6331
Z
Dcalcd/g cm−3
μ/mm−1
F(000)
θmax/°
Collected
Unique reflns
Obsd reflns
[I > 2.0σ(I)]
No. of variables
GOF
R
wR
Rint
5961
6598
5521
416
1.170
0.0767
0.1245
0.0738
0.253, −0.411
396
1.007
0.0470
0.1033
0.0490
0.554, −0.349
384
1.070
0.0578
0.1320
0.0510
0.431, −0.420
Largest diff.
peak, hole/e Å−3
Table 3 The selected bond lengths (Å) and bond angles (°) for complexes 1–4
Bond lengths
Ln1–N1
Ln1–N2
Ln1–N3
Ln1–N4
1
2
3
4
2.303(3)
2.383(3)
2.222(3)
2.249(3)
2.272(2)
2.300(2)
2.375(3)
2.436(3)
2.298(2)
2.365(2)
2.232(2)
2.246(2)
2.317(6)
2.298(6)
2.236(6)
2.239(6)
Bond angles
N3–Ln1–N4
N3–Ln1–N1
N4–Ln1–N1
N3–Ln1–N2
N4–Ln1–N2
Acknowledgements
110.09(11)
123.31(11)
103.72(11)
97.04(11)
110.45(9)
128.31(9)
104.65(9)
96.03(9)
109.47(9)
123.27(9)
103.93(9)
100.31(9)
140.05(9)
116.6(2)
113.2(2)
121.9(2)
114.5(2)
103.9(2)
Financial support from the National Natural Science Foun-
dation of China (grants 21174095, 21172195, and 21132002),
PAPD, and the Qing Lan Project is gratefully acknowledged.
143.93(10)
142.53(9)
Table 4 The selected bond lengths (Å) and bond angles (°) for complexes 6–8
Bond lengths
Ln1–N1
Ln1–N2
Ln1–N3
Ln1–N4
6
Bond lengths
Ln1–N1
Ln1–N2
Ln1–N3
Ln1–N4
7
Bond lengths
Ln1–N1
Ln1–N2
Ln1–C24
Ln1–C25
Al1–C26
Al1–C27
8
2.323(4)
2.352(3)
2.255(3)
2.225(3)
2.370(3)
2.349(3)
2.275(4)
2.253(4)
2.425(3)
2.339(3)
2.277(3)
2.548(5)
2.573(5)
1.960(5)
1.966(5)
Ln1–O1
Bond angles
N4–Ln1–N3
N4–Ln1–N1
N3–Ln1–N1
N4–Ln1–N2
N3–Ln1–N2
N1–Ln1–N2
Bond angles
N3–Ln1–N4
N3–Ln1–N1
N4–Ln1–N1
N3–Ln1–N2
N4–Ln1–N2
N1–Ln1–N2
N4–Y1–O1
N3–Y1–O1
N2–Y1–O1
N1–Y1–O1
Bond angles
N1–Ln1–N2
C24–Ln1–C25
C24–Al1–C25
C26–Al1–C27
110.09(13)
121.65(13)
104.76(13)
99.99(12)
139.21(13)
80.58(12)
124.45(17)
105.83(13)
101.92(13)
127.68(13)
104.60(14)
77.77(12)
87.66(12)
82.99(12)
81.88(11)
159.11(11)
80.66(10)
82.31(17)
109.0(2)
117.6(2)
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Table 5 The polymerization of isoprene with complexes 1–9 under activation of organic borate and trialkylaluminiuma
Entry
Cat
[IP]/[Ln]
[Ln]0/[Al]0/[Bc]0
Time
Yield (%)
Mn(× 104)b
PDIb
1,4c (%)
1
2
3
4
1
1
2
3
3
3
4
4
4
4
4
4
5
6
6
6
7
7
7
7
7
7
8
8
9
9
1000
2000
2000
500
1000
2000
1000
2000
500
1000
2000
3000
2000
2000
2000
2000
500
1000
2000
3000
2000
1000
1000
1000
2000
2000
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/5/1
1/0/1
1/0/0
1/5/1
1/5/1
2 min
5 min
10 min
5 min
2 min
10 min
1 h
100
100
58
100
40
28
53
19.7
25.1
11.0
12.7
19.7
24.2
79.1
63.9
37.4
47.4
82.1
105.6
35.1
36.1
37.5
37.8
21.8
34.3
69.4
118.1
55.6
97.9
99.7
/
1.41
1.79
1.60
1.53
1.41
1.99
1.65
1.51
1.80
1.88
1.84
1.86
1.31
1.95
2.11
2.06
1.87
1.92
1.63
1.93
1.74
1.78
1.91
/
91.0
89.3
91.7
88.4
87.7
87.7
91.7
91.7
89.3
89.3
88.5
87.7
89.3
92.6
92.6
90.9
93.4
92.6
91.7
91.7
91.9
92.5
93.4
5
6
7d
8d
9
3 h
26
2 min
2 min
3 min
2 min
4 min
3 min
5 min
5 min
2 min
2 min
3 min
3 min
5 min
40 min
40 min
4 h
100
100
100
100
71
10
23
10
11
12
13
14
15
16e
17
18
19
20
21e
22d
23
24
25
26
20
100
100
100
100
37
43
47
0
11
34
3 min
10 min
44.6
78.7
1.92
1.93
89.3
89.3
a Polymerization conditions: in toluene; Ln 15 μmol; AliBu3 75 μmol; BC 13.8 mg (BC = [Ph3C][[B(C6F5)4]); 1/5 (v/v) isoprene–toluene; 25 °C.
b Determined by GPC in THF at 40 °C against a polystyrene standard. c Determined by 1H NMR in CDCl3. d AlMe3 was used instead of AliBu3.
e The addition sequence: Ln, then BC, last AliBu3.
B. A. Messerle, Organometallics, 2011, 30, 5978;
(o) M. P. Weberski, C. Chen, M. Delferro, C. Zuccaccia,
Notes and references
1 (a) A. L. Gavrilova and B. Bosnich, Chem. Rev., 2004, 104,
349; (b) H. Li and T. J. Marks, Proc. Natl. Acad. Sci. U. S. A.,
2006, 103, 15295; (c) V. Ritleng and M. J. Chetcuti, Chem.
Rev., 2007, 107, 797; (d) S. Singh and H. W. Roesky, Dalton
Trans., 2007, 1360.
A. Macchioni and T. J. Marks, Organometallics, 2012, 31,
3773; (p) W. Y. Li, W. T. Wu, Y. R. Wang, Y. M. Yao,
Y. Zhang and Q. Shen, Dalton Trans., 2011, 40, 11378;
(q) W. Y. Li, Y. M. Yao, Y. Zhang and Q. Shen,
Chin. J. Chem., 2012, 30, 609.
2 (a) D. R. Moore, M. Cheng, E. B. Lobkovsky and
G. W. Coates, J. Am. Chem. Soc., 2003, 125, 11911;
(b) M. J. McNevin and J. R. Hagadorn, Inorg. Chem., 2004,
43, 8547; (c) B. M. Trost, A. Fettes and B. T. Shireman,
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